Surgical treatment with the aid of image-assisted navigation systems, also called tracking systems, is known in principle. Such a system is, for example, described in DE 196 39 615 C2 and the associated U.S. Pat. No. 6,351,659 B1. Other surgical navigation systems are known, for example, from U.S. Pat. Nos. 4,722,065, 4,791,934 and 5,383,454. Based on data from imaging methods, such as computer tomography, nuclear spin tomography and x-ray transillumination, a number of navigation systems and/or tracking systems use the captured recordings of body parts for a visual and absolute spatial representation of surgical instruments in relation to body parts, such as tissues or bones. In order to ensure the spatial representation of surgical instruments with respect to the patient inside the operating theatre, the coordinate system of the diagnostic data, for example, a computer tomograph, which is fixed by the imaging unit/scanner, has to be aligned with and superimposed onto a second coordinate system assigned to the patient in his actual position in the operating theater. Assigning or aligning the appropriate body structures in the image data set to the patient's actual position in the operating theatre is commonly referred to as registering.
Such registering is usually achieved by a superimposing method, with the aid of anatomical landmarks or special marking points or markers. The data set points are assigned to the real points by means of “paired point matching” or by surface matching between the patient's anatomy and 3D surfaces of the data set. The points existing in the data set are aligned with corresponding points of the patient, i.e., artificial or natural surface points. Once the coordinate systems have been aligned, i.e., once the patient has been registered, the position of a surgical instrument, localized in the patient coordinate system by means of an optical, magnetic or ultrasound-based localization system, can also be represented spatially on the computer screen, positionally exact in the co-ordinate system of the diagnostic data set, and used to assist in the treatment.
The known methods are based on such co-registration of image data set (CT/MRT) points and patient points, points within the image data set or space being used as absolute reference points. During registration, these absolute reference points are aligned with identical points, which can be identified on the “surface” of the patient.
Disadvantageously, such registration methods cannot be applied in cases in which the image data set only comprises an internal area of the body or only parts of the anatomy (for example, only vessels). One problem is that these internal areas of the body often do not comprise any natural landmarks (for example, in the patient's brain) and also cannot easily be provided with artificial landmarks. Therefore, these volume data sets cannot be registered using the conventional methods. They are, however, important in, among other areas, vascular surgery in which high-resolution image data sets indicate an exactly defined, internal body volume in which the vascular disease (for example, an aneurysm) and the exact vascular paths are situated. Previously, such visualizations from image data sets for internal areas of the body have only been used separately as a source of information of the operating surgeon, i.e., the information available form them was, for example, viewed by the physician beforehand, but remained unused as far as the patient present in the operating theatre was concerned.